1. Field of the Invention:
The subject invention relates to sealing devices, and more particularly, to a floating wiper seal assembly for a reciprocating shaft in a hydraulic pump or cylinder that can accommodate shaft-to-bore misalignment.
2. Description of the Prior Art:
In a hydraulic system, fluid pressure is converted to linear force by applying the fluid pressure to an end of a reciprocating shaft or piston which slides axially in a matching bore of a cylindrical housing or crankcase. A connecting rod extends from the piston out through the power end of the bore. To avoid loss of fluid and fluid pressure from the system, it is necessary to provide a sealing device between the connecting rod and the power end of the bore.
In some applications, e.g., in large earth moving vehicles, such as tractors, loaders, off-highway trucks, and the like which employ hydraulic jacks and/or suspension struts, piston cylinders are exposed to all varieties of dirt, debris, moisture and other abrasive contaminants. It is well known that such contaminants are injurious to the seals, bearings and other components of such jacks or struts. Accordingly, it has been the practice to use rod wipers to wipe the piston rod clean as it is retracted into the cylinder so as to reduce to the maximum extent possible the amount of contaminants reaching the seals and bearings. U.S. Pat. Nos. 3,866,923 and 4,618,153 both disclose rod wipers for this purpose.
In order to satisfactorily perform the desired wiping function, such wipers must remain in continuous wiping contact with the piston rod as it moves back and forth through the wiper. Also, the wiping contact must be applied with a sufficient radial force to ensure the desired cleaning action on the rod. These tasks may be complicated where extreme side loads are exerted on the rods of hydraulic cylinders in operation, which causes the rapid radial displacement of the rod relative to the wiper as the rod moves axially in and out of the cylinder. Prior wipers have been made of rubber to attain this necessary resiliency and responsiveness. However, rubber is relatively soft and susceptible to a high wear rate. Harder plastic materials, such as polyurethane for instance, exhibit much greater wear resistance.
Unfortunately, two problems exists with the use of such harder materials. First, harder materials have lower creep resistance. This allows the radial force they exert on the rod to lessen over time, allowing debris to get past the wiper. Second, they have a much lower response rate, particularly at extremely low temperatures, due to their higher flex modules and decreased resiliency at extremely low temperatures. In other words, such materials do not respond quickly enough to afford their movement with the rapid radial displacements of the rod. This causes the wiper to leave contact with the rod and also allows debris to get past the wiper.
Further, conventional seals such as outer periphery lip type oil seals with or without substantial wiping contact, as well as V-ring or braided packing sets which are also currently used depending upon the application, provide less than satisfactory service. In most cases, the reciprocating shafts or piston rods are misaligned or exhibit cycloidal side movement as they pass through the sealing device at high cycling rates. These conventional seals are rigidly mounted in a seal housing to provide a static seal around their outer periphery and their bodies cannot flex enough to permit their sealing surfaces or lips to remain in constant dynamic sealing and where applicable, on their inner periphery, in wiping contact with the shaft. The result is oil and/or contamination leakage. Examples of such lip seals are shown in U.S. Pat. Nos. 5,303,935, 5,205,568 and 5,288,086.
Other seals having a convoluted (flexible) cross-section design and a bearing insert to help the sealing surface follow the shaft have shown improved service in a few cases. An example of this type seal is shown in U.S. Pat. No. 4,553,760. However, the use of such seals is limited as there often is not enough cross-sectional space to design a convoluted body that will provide enough flexibility.
The present invention is directed to an improved highly flexible wiper seal device for use in a hydraulic pump system to effectively seal the power side of the oil crankcase or reservoir of the pump during the power stroke, while wiping the reciprocating shaft of the pump system on the return stroke to preclude contamination of the system with debris.